From f39ccb1a90a3c77be09fd752a8c59ae5478b45dc Mon Sep 17 00:00:00 2001
From: Ronen Friedman <rfriedma@redhat.com>
Date: Tue, 2 Aug 2022 08:40:18 +0000
Subject: [PATCH] osd: a faster version of SnapMapper::get_prefix()

Using fmtlib, and treating the size of uint64_t as a known
quantity.
Per google-bench - the new version is 10% to 20% faster.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>
---
 src/osd/SnapMapper.cc | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/src/osd/SnapMapper.cc b/src/osd/SnapMapper.cc
index 804213b1f2644..26ace62a7382e 100644
--- a/src/osd/SnapMapper.cc
+++ b/src/osd/SnapMapper.cc
@@ -13,6 +13,7 @@
  */
 
 #include "SnapMapper.h"
+#include <fmt/printf.h>
 
 #define dout_context cct
 #define dout_subsys ceph_subsys_osd
@@ -99,13 +100,11 @@ int OSDriver::get_next(
 
 string SnapMapper::get_prefix(int64_t pool, snapid_t snap)
 {
-  char buf[100];
-  int len = snprintf(
-    buf, sizeof(buf),
-    "%lld_%.*X_",
-    (long long)pool,
-    (int)(sizeof(snap)*2), static_cast<unsigned>(snap));
-  return MAPPING_PREFIX + string(buf, len);
+  static_assert(sizeof(pool) == 8, "assumed by the formatting code");
+  return fmt::sprintf("%s%lld_%.16X_",
+		      MAPPING_PREFIX,
+		      pool,
+		      snap);
 }
 
 string SnapMapper::to_raw_key(
-- 
2.39.5